The acoustics of the khaen, bawu, and gourd pipe

Abstract

Mouth-blown instruments using a free reed coupled to a pipe resonator have a long history in China, Japan, and throughout Southeast Asia. The khaen and the gourd pipe are unusual wind instruments, employing a free reed mounted in the side of a cylindrical tube open at both ends, although in the gourd pipe the player has the option of closing the bottom of the pipe so that the reed is near the closed end. The bawu is a closed cylindrical pipe with a free reed at one end, in which the effective acoustical length is varied by the use of tone holes. The playing frequency of each pipe of the khaen or the gourd pipe is typically slightly above both the resonant frequency of the pipe and the natural frequency of the reed. In the bawu, on the other hand, the pipe resonance pulls the sounding frequency well above the natural reed frequency, resulting in a striking difference in tone quality. Acoustical measurements made on these instruments include studies of reed vibration and impedance measurements of the pipes, with particular attention to the coupling of the reed vibration with the pipe resonator.